The invention is directed to the joinder of materials and particulary to the joinder of structural material formed from carbon-carbon composites.
This invention concerns threaded fastening members. A major problem involved in the use of threaded fastening members is that of loosening or relaxation caused by stress or by vibration. Another problem is the fracturing or other damage to the materials to be joined by the fastener being tensioned.
Generally to overcome the first of these problems, the threads of the fastener are coated with a sealing or locking compound. An example of locking the threads inplace in this manner is taught by the following patents.
U.S. Pat. No. 3,814,156 teaches coating the threads with a microencapsulated liquid adhesive and a torque tensioning agent which brings the torque-tension relationship of the coated threaded member to a minimum of approximately 80% of the torque-tension relationship of the threaded member without the coating.
U.S. Pat. No. 4,191,677 teaches placing a patch of unpolmerized thermoplastic polymer on the threaded fastener as a liquid which is spread over the threads when threaded and allowed to cure at room temperature after the fastener is set. The Patent teaches away from using heat on the threaded member.
U.S. Pat. No. 4,132,815 teaches a method similar to the last referenced Patent except heat is applied to the threaded area to facilitate cure.
U.S. Pat. No. 4,576,847 teaches the use of a threaded member constructed of a fiber-reinforced plastic coated with a crosslinked resin. The resin is caused to crosslink by the addition of an organic acid.
One of the most pressing challenges in the development of carbon-carbon composite material as a structural material for aerospace application, is the joining and fastening of the various airframe elements. A bolt type fastener can be obtained but the machined threads in the carbon-carbon and high torque required to seat the bolt often exceeds the load carrying capability of the composite threads. This is especially true when large number of fibers are severed during the machining of the threads. An alternate and unique method proposed herein, relies on friction and a large preload to secure a collar unto a bolt shank.